Method of producing monocalcium phosphate containing a high p2o5 content



Patented July 11, 1950 =10 F H C l METHOD OF PRODUCING MONOCALCIUM"PHOSPHATE CONTAINING A HIGH P205 CONTENT NoDrawing.

This invention relates to a granular, free flowing, substantially,non-caking monocalcium phosphate having a high P205 content and to aprocess for producing same.

Monocalcium phosphate containing an excess of P205 corresponding to 1%by weight of free H3PO4 is very hygroscopic and tends to cake and loseits dry free flowing character in a relatively short time. If the P205content of this product is increased to a value corresponding to 5% freeacid, its hygroscopicity is markedly increased with the result that,upon storage, it rapidly sets to a solid crystalline mass.

To offset these objectionable properties it has been the practice toeither neutralize the excess acidity or to so proportion the rawmaterials used in the preparation of monocalcium phosphate that theproduct containsless'than 1% by weight of free acid. These methods ofstabilization serve the intended purpose very well except that thepotential acidity and also the solubility of the monocalcium phosphateare too low for certain applications. For example, in the beverageindustry there has recently been a demand for a granular, free flowing,monocalcium phosphate of high acidity and solubility which may be usedin partial or complete substitution of fruit acids such as citric,tartaric, and malic acid and the like. In view of its low acidity andsolubility in aqueous media, commercially availablemonocalcium phosphateis not suitable for this purpose and, so far as I am aware, theseproperties cannot be improved by the prior art methods without, at thesame time, excessively increasing the hygroscopicity and caking tendencyof the product.

It is therefore the object of the present invention to provide aprocessfor making a granular, free flowing, substantially non-cakingmonocalcium phosphate which is readily soluble in aqueous media andwhich contains P205 in an amount corresponding to a free acid (H3PO4)content of from 5% to 18.5% and preferably fromabout to about 18.2% byweight.

In carrying out the present invention, phosphoric acid is thoroughlymixed with granular v lar, free flowing and substantially non-cakingmonocalcium phosphate of high acidity is produced which is adapted foruse as a fruit acid substitute in the production of powdered beverages.

For a more complete understanding of the pres- Application December 22,1945, Serial No. 637,094

5 Claims. (or. 23409) I 7 ent invention, reference is made to thefollowing specific examples.

EXAMPLE I 36 lbs. of H3PO4 was gradually added and mixed in aBaker-Perkins mixer with 100 lbs. of spray dried monocalcium phosphatehaving the following screen analysis Per cent +80 0.8 80-]-200 20.4 20079.6

After about 3 to 5 minutes, the mixing operation was completed and thenthe product was put through a 4 inch vibrating screen to break up anylumps which were formed. The screened product was dried in a stainlesssteel rotary drier heated with hot air at C. to C., whereupon it wasmilled in a hammer mill and finally passed through a 10 mesh screen. Theresulting product was granular, free flowing and substantially noncakingin character and on analysis was found to have the following P205, freeH3PO4 and moisture content:

' Per cent P205 60.69 Free H3PO4 15.74 Loss at C a; 2.92

EXAMPLE II 36 lbs. of 80.7 of H3PO4 was thoroughly mixed with 100 lbs.of spray dried monocalcium phosphate oversize using a mixing time ofabout 50 seconds. The resulting mixture was passed through a 4 inchvibrating screen to break up a relatively smallproportion of lumps andthen dried in a rotary air drier at a temperature of 95 C. The driedmixture was milled in a hammer mill and finally put through a 10 meshscreen. The product thus obtained was granular, free flowing andsubstantially non-caking in character and was further characterized bythe following EXAMPLE III The procedure set forth in Example II wasrepeated using 43.5 lbs. instead of 36 lbs. of 80.7% H3PO4.

3 The m'onficalcium phosphate huspr pa d Wa tivelycoarseas compared withthe monocalcium dry, granular, free flowing and substantiallynonphosphate;.,used in preparing the phosphoric acid caking in characterand had the following chemimix, thus demonstrating that agglomerationcal and screen analysis: :-.',.;takes place in the mixing and rotarydrying steps.

This is-iurtherzconfirmed by the fact that exami- Y I I 1 nation underavmicroscope shows that these prod- =3 28 I note consistofv clusters ofgranular monocalcium C310 3 p phosphate. e 1 =1 2-% fThe' variousconditions of operation of the present processwill now be discussed ingreater Screen analyszs a v 4 v .detail. R10 Trace Chemical analysis:

hemonocalc'ium phosphate and phosphoric CRZO "per cent 60.0 ac diaremixed in the proportions calculated to CR50 do 88:0 -yielda productcontaining P205 in an amount corc380 do 94.0 responding to a free H3PO4content of from 1 to $80 do 6.0 18.5%. "Whenzaxfruit acid substitute isdesired,

1 the fRzOs -content of the product is .restrictedto EXAMPLE IV a va'lueequivalent ton, free :acid content of from Four atc o mOHOGaICiHmphosphate Were 10% to 18.3% H3PO4 and within this :rangea P205 p paredby m x o r in a Baker-Perkins 1 content equivalentto14% 'H3PO4 ispreferred.

mixer for 1 minute 36lbs. of 80.72% H3PO4= and t The mixing operation iscarried out by adding I 100 lbs. of monocalcium phosphate having the andmixing phosphoric "acid it monocalcium following Chemical and screenanalysis: phosphate withinfaiperiod of from 0.5 to 51-minutes, but themost satisfactory results are 'ob- Regular Granular SemigranularOversize tained by using .a mixing time Of about '1 :minute.

' 4 The particle size of the monocalcium phosphateplays animportantrolein determining the free flowing, non-cakingcharacter of the product. Ingeneral, when the product is to be used CHEMICAL ANALYSIS CaO v23. 6023.12 23. 3e 23. 24

P205 5594 5576 5576 5585 iii-the preparation of beverage powders,the ma-Ignition Loss 20.51 20.08 20.29 20. e7 -jor proportionof the monocalciumphosphate Total 100m 98% 9941 9 used in making the phosphoric acid mixshould have a particle size of not less than 200 mesh,

SCREEN ANALYSIS preferably not lessthan 100 mesh, and notzgreater than'10 mesh. For optimum results, substantially all 'of the "monocalciumphosphate should 0 0 1.5 8 0 o 4.8 pass through a: 10 mesh screen and beretained 3:12 by'a 50mesh screen. 38.2 98.8 50.6 98.0 Afterthe'monocalcium phosphate and :phos- 8 0 40 phoric acidhave'beenintimately mixed, the'prodnot is put'through a coarse vibrating"screen or he foregoing miXtures Were passed through a another suitabledevice to break up any :lumps 1A} inch Vibrating Screen and then dried apresent rotary kiln with air heated to approximately 80 The Screenedthen dried it 0. The dr ed prfiducts W analyzed and found perature offrom 60 :C.'t'o 100 .C. and preferably to have the following chemicaland screen analyt 't t from 99 C t 1 0 15, the numerals l, 2', 3 anddesignating the The drying 'operation'may be carried out under productsmade from Samples 3 and 4 atmospheric or reduced'pressure and when thespectively. latter procedure is employed, the product is preferablyheated at a temperature of from C. to 1' 2' 3" 4' C while beingsubjected to an absolute pressure of 20 millimeters of mercury. CHEMICALANALYSIS Any suitable equipment may be employed in this step of theprocess, but I prefer to dry the P 0 g 54 3g 55 product in a stainlesssteel rotary drier heated Iniiifiis's'i- 25135 25116 24:80 25110 Wlthhot F at to The dr1ed' product is milled in a hammer mill or anothersuitable mill to breakup whatever lumps may be formed. At the completionof this 60 operation, the :product is screened to the desired size. Whenthe product is to be used as a fruit Total 100.00 100.08 99.90 100. 45

SCREEN TEST 23:3 lgg 23 2 33 acid substitute in'the preparation of watersolugg 38% 33-2 g gble beverage powders the milled product is passed 9 10:0 100: 100:0 a Screen.

tr tr 65 .By properly :sel'ecting relatively coarse monocaiciumphosphate, theinitial screening and also The above products were milledin a hammer the milling steprmay be omitted. Therefore, mill andscreened to remove plus 10 mesh mastated broadly, the present processinvolves interial, thus yielding in each case a readily solutimatelymixing phosphoric acid with monocalble, granular, free flowingsubstantially non-cak- 7 cium phosphate, drying the resulting mixtureand. ing monocalcium phosphate having a high conthen screening the driedproduct to the desired tent of P205. These products were found to besize. particularly suitable for use as fruit-acid substi- -Theproductsofzthe present invention are readtutes in the production-of powderedbeverages. ily soluble in aqueous media and possess a high The productsof the present invention are'rela- 15 content of freed-13204; inaddition they are granular, free flowing and substantially non-caking incharacter and may be stored indefinitely in closed containers withoutencountering an appreciable amount of lumping. They are distinguishedfrom the monocalcium phosphate of the prior art in that they combine allof the foregoing properties in a single product.

The foregoing detailed description has been given for the purpose ofillustrating the preferred methods of carrying out the invention and itshould be clearly understood that the invention is not restrictedthereto.

I claim:

1. The method of producing a readily soluble, granular free flowing,substantially non-caking composition consisting of monocalcium phosphateand 15.74% by weight of free H3PO4, which comprises intimately mixingtogether for 3 to 5 minutes 100 lbs. of spray dried monocalciumphosphate having the following screen analysis Per cent and 36 lbs. of80% H3PO4, passing the resulting mixture through a inch vibratingscreen, drying the screened product in a rotary drier heated with hotair at 90 C. to '100 C., milling and then screening the dried productthrough a 10 mesh screen.

2. The method of producing a readily soluble, granular, free flowing,substantially non-caking composition consisting of monocalcium phosphateand 18.2% by weight of free H3PO4, which comprises mixing together forabout 50 seconds 100 lbs. of spray dried monocalcium phosphate oversizeand 43.5 lbs. of 80.7% H3PO4, passing the resulting mixture through a A.inch vibrating screen, drying the screened product in a rotary drier ata temperature of 95 C., milling and then screening the dried productthrough a 10 mesh screen.

3. The method of producing a readily soluble, dry, agglomerated, freeflowing, substantially non-caking composition consisting of monocalciumphosphate and from 5% to 18% by weight of free H3PO4, which comprisesintimately mixing together for 0.5 to 5 minutes spray dried monocalciumphosphate and phosphoric acid in the proportions calculated to yield theabove composition, passing the mixture through a A inch screen, dryingthe screened product, milling and then screening the dried productthrough a 10 mesh screen, said monocalcium phosphate prior to admixturewith said phosphoric acid having a particle size of from +200 mesh to 10mesh.

4. The method of producing a readily soluble, dry, agglomerated, freeflowing, substantially non-caking composition consisting of monocalciumphosphate and from about 10% to about 18% by weight of free H3PO4, whichcomprises intimately mixing together for 3 to 5 minutes spray driedmonocalcium phosphate and phosphoric acid in the proportions calculatedto yield the above composition, passing the mixture through a 4 inchscreen, drying the screened product in a rotary dryer with air heated toa temperature of from C. to 100 C., milling and screening the driedproduct through a '10 mesh screen, said monocalcium phosphate prior toadmixture with said phosphoric acid having a particle size of from +200to 10 mesh.

5. The method of producing a readily soluble, dry, agglomerated, freeflowing, substantially non-caking composition consisting of monocalciumphosphate and about 14% by weight of free H3P04, which comprisesintimately mixing together for about 1 minute spray dried monocalciumphosphate and phosphoric acid in the proportions calculated to yield theabove composition, passing the mixture through a inch screen, drying thescreened product in a rotary dryer with air heated to a temperature offrom C. to C. milling and screening the dried product through a 10 meshscreen, said monocalcium phosphate prior to admixture with saidphosphoric acid having a particle size of from +50 to 10 mesh.

WILLIAM L. ROBINSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,442,318 Whittier Jan. 16, 19231,538,910 Stokes May 26, 1925 1,924,137 Stokes Aug. 29, 1933 2,291,608CobbS Aug. 4, 1942 2,332,735 Lyons Oct. 26, 1943 2,424,992 Lee Aug. 5,1947 FOREIGN PATENTS Number Country Date 330,777 Great Britain June 19,1930 426,472 Great Britain Apr. 1, 1935

1. THE METHOD OF PRODUCING A READILY SOLUBLE, GRANULAR FREE FLOWING,SUBSTANTIALLY NON-CAKING COMPOSITION CONSISTING OF MONOCALCIUM PHOSPHATEAND 15.74% BY WEIGHT OF FREE H2PO4, WHICH COMPRISES INTIMATELY MIXINGTOGETHER FOR 3 TO 5 MINUTES 100 LBS. OF SPRAY DRIED MONOCALCIUMPHOSPHATE HAVING THE FOLLOWING SCREEN ANALYSIS